Rubber composition containing an amidine nitrite and method of preparing cellular product therefrom



' uct.

Unit d. ta Patent RUBBER COMPOSITION CONTAINING. AN AMI- DINE NITRITE AND METHOD OF PREPARING CELLULAR PRODUCT THEREFROM Hans Z. Lecher, Plainfie ld, and Frederic H. Adams, Bound Brook, N.J.,'assignors to American Cyanamid Company, New York, N.Y., a corporation of Maine No Drawing. Firearm 25,1957, Ser. No. 667,955

10 Claims. c1. zap-2.5

The present invention relates to cellular organopla'stic' materials. More particularly, it relates to a method of preparing such cellular organoplastics using a new class of blowing agents comprising amidine nitrites,

In the manufactureof cellular organoplastics, a blowing agent is incorporatedintothe uncured material and the mixture subjecte'd'to curing. The gaseous decomposition product thus released blows the organoplastic formingminute cells throughout. Certain properties make a successful blowing agent. should be stable on storage, shipment and handling but should be unstable at the curing temperature without decomposing explosively. It should disperse evenly or dissolve in the uncured organoplastic to permit formation of fine uniform cells. A blowing agent and its decomposition product shouldbe nontoxic and odorless.

In preparing cellular rubber, decomposition of the blowing agent should occur only after vulcanization has partially proceeded so that the rubber stock has sufiicient strength to retain the gaseous decomposition prod- Decomposition, however, must occur before vulcanization proceeds to such an extent that cell formation isrestricted. Complete evolution. of gas should occur prio'rto completion of vulcanization. to produce a blown product of as low density" as possible. Still further, the blowing agent must not interfere with rubber vulcanization accelerators or other additives, or itself substantially accelerateor retard the vulcanization proc'essi.

' Both inorganic and organic compounds have been employedtas blowing agents. Among these might be men-v I tioned various inorganic. nitritessuch as ammonium' nitIitEySOdilll'l'l nitrite with an ammonium salt, and carbon ates'such. as; ammonium carbonates. Generally, how ever, these are unstable and produce undesirable changes in the material treated. Particularly detrimental to, rubber are the largequantities of oxides of nitrogen evolved in thedecomposition of these inorganic nitrites. Also; the carbon dioxide evolved,- when a carbonate such as ammonium carbonate is used, is also objectionable because of its rapid diffusion rate out of the rubber.

It has now been found, in accordance with the present A blowing agent 2. 11. 2 V V Patented Mar.

xylyl guanidine nitrites, N-monoand N,N-dibenzyl-t guanidine nitrites and inorpholino, "piperidino and furfurylamino guanidine nitrites, big uanide nitrite and its corresponding derivatives, and guanylurea nitrite and its I corresponding derivatives.- r v I v f Anadvantage of the present inventionis that the new class of blowing agents may be prepared by known metli i ods. They may be prepared froman amidine salt, the cation of the acid being so chosen as to give an insoluble precipitate when the amidinesalt is reacted with a metal nitrite. Alternatively, the hydrochloride of the amidine" may be reacted with an alkali metal nitrite followedbyi evaporation and subsequent extraction of the amidine ni trite with alcohol or other'suitable organic solvents, in which it is soluble. I V The blowing agents of this invention may be employed for blowing rubber as well as plastic materials. By rubher is meant natural rubber as well as synthetic rubberlike polymers of butadiene-il,3 and substituted butadienes such as methyl-Z-butadien lj, chloro-2-butadiene-l,3 and the like. 7 In additiomit is intended to includepcopolymersof butadiene-1,3 with a polymerizable compound containing an olefinic linkage such as acrylonitr-ile; styrene, acrylamide, isobutylene and the like. By plastics is meant-pflymeri'zed Vinyl and acrylic ompoundspom i merized 'olefins, cellulose esters, cellulose ethers, poly- 1 ester resins, epoxy resins, urea-aldehyde resins, phenoll aldehyde resins and the like. By the term organ'oplastic used in accordance witlrthis invention, it is meant to includeall of these. V V

The amount of blowing agent employed in accordance v r with this invention will vary according to thetype' of j.

. amount'of blowing agent employed in themanufacture of cellular rubber will vary from about 0.5%"to' about vinyl polymers and the: like, theamount of blowing agent; will generally be greater than that necessary in rubber.

.. degree of blow and the like.

' examples, which are intended to be illustra'tive only and invention, that cellular products of excellent character- V istics may be obtainedby using amidine nitrites as blowing agents; These compounds may be represented by the dine nitrites,. .Nmo'no' and .N,N-di-phenyl, V tolyl and.

. 126 parts of barium nitrite monohydrate, of], 9 8.3% purity, is dissolved in 400 parts of water atiap'proxir'nately 45"; C. and added with stirring to the solutiojnrof got;

a, and then filtered hot. .crystalsofegguaiylu product to be blown as well as the'degr'ee Of'blOVt/d sired. Thus in the manufacture of cellularrubberpro ucts, whether natural rubberor synthetic polymers and'c polymers such as polymerized butadiene l,3,' copoly merized butadiene-styrene, butadiene-acrylonitrile' and the like, as'little as 0.5% by weight on the'rubber may-be, i employed, Products of decreasing densities are obtained- ,7 using greater-amounts-of blowing agent. In general; th'e' 5% on the rubber, usually between about 1% and i:3%. i i In the manufacture'of cellular'plastic materials, such-,;f or; instance, as urea-aldehyde resins, phenolaldehyde resins',

In general, this amount will run from about 50% to about 30% by weight on the resin, depending. again on the particular blowing agent, the resin to 'be blown,

The invention is further demonstrated by the rditswi not by way of limitation. Unless otherwise specifi parts are by weight;

" "EXAMPLEI G uanylurea nitrite i 169 partsof guanylurea sulfate are dissolved in l0j00 parts of water by heating -to approximately f C; jand made slightly alkaline. with sodiur'n'hydroxide solutio urea sulfate at about 80-9090. After stirring; temperature for 3.0 minutes, 40,: partsfof,vdiatomac earth are added, the mixture'stirred'for 091' at-90" C. a solution of 252 parts of 98.3% pure barium nitrite monohydrate dissolved in 200 parts of water. 40 parts of diatomaceous earth are then added and the mixture filtered.. The filtrate iscooled and evaporated to obtain 180 parts of biguanide nitrite. decomposition about 185186 C.

EXAMPLE 3 Phenylbiguanide nitrite 1am NH-NHO: cmmn-c-mi- -NH1 21.4 parts of phenylbiguanide hydrochloride are dissolved in 250 parts of water at 70 C. To this is added 7 parts of sodium nitrite solution and the solution evaporated to dryness. The residue is extracted with 200 parts by volume of boiling alcohol. On cooling the phenylbiguanide nitrite separates and is isolated by filtration and dried. Melting point is 188 C. with decomposition.

EXAMPLE 4 Guanidine nitrite NH-HNOa 180.1 parts of guanidine carbonate are dissolved in 325 parts of water at about 50 C. and the resulting solution clarified by the addition of diatomaceous earth and decolorizing carbon and filtered. T o the filtered solution is then added a solution 138.2 parts of sodium nitrite dissolved in 200 parts of water. The mixture is evaporated to dryness and then boiled up with 400 parts of denatured alcohol and the mixture filtered. On cooling the filtrate a small amount of guanidine nitrite crystallizes out. The remainder of the solution is evaporated to one-half its volume, cooled to 5 C. and a larger crop of crystals obtained. Yield of product is 60.2 parts, M;P. 99-110 C.

EXAMPLE 5 Acetamidine nitrite NH-ENO:

CHa-C- N HS 46.2 parts of silver nitrite is ground up fine inamortar with 400 parts of water. This slurry is then mixed with a. solution of 28.4 parts of acetamidine hydrochloride and 100 parts of water. The mixture is stirred for 1 hour at room temperature and the curdy white precipitate of silver chloride filtered off. The filtrate is evaporated to small volume and the yellowish crystals filtered oft and dried at 50 C. These crystals, 24.7. parts, are recrystallized from approximately parts of alcohol after boiling with Melting point with complete. The precipitated silver chloride is then filtered ofi and the filtrate evaporated to small volume and cooled; The product, butyramidine nitrite, crystallizes out and is further purified by recrystallization from alcohol.

EXAMPLE 7 Benzamidine nitrite The procedure of Example 3 is repeated replacing phen-- ylbiguanide hydrochloride with an equivalent amount of benzamidine hydrochloride. Benzamidine nitrite, MP.

6-t-butylphenol).

diatomaceous earth and decolorizing carbon. The puri- I fied product is a white. crystalline material which melts with decomposition between 155160 C.

EXAMPLE 6 Butyramidine nitrite NH-HNO: cmomcm -Nm ture is stirred at room temperature until the reaction is" 70 C., is recovered. EXAMPLE 8 Rubber stocks are compounded according to the following composition:

Compound:

Plasticized smoked sheet 2,2'-methylene-bis(4wmethyl-6-t-butylphenol) 0.5

Stearic Acid Guanylurea nitrite, biguanide nitrite, guanidine nitrite, and acetamidine nitrite are employed as blowing agents. Each stock is blown at C. for 60 minutes.

(51 grams) is blown in each instance. Complete blows 'are obtained except in the case of biguanide nitrite in which the corners are slightly rounded. Cell size is fine forthose products blown with biguanide nitrite and acct-- amidine llltllte' and medium-fine in the products blown with guanylurea nitrite and guanidine nitrite.

EXAMPLE 9 To illustrate the blowing of plastics, 5.0% 'guanylurea nitrite is incorporated in Bakelite polyethylene DYNH along with 0.1% antioxidant 2,2'-methylene-bis(4-ethyl-' A 200% expansion load (51 grams)- is blown in a 6 cubic inch mold at C. for 20 minutes.

A complete blow is obtained, the blown product having medium fine cells.

We claim:

taining an amidine'm'trite of the formula in which R' is selected from the group consisting of' alkyl, aryl, aralkyl, amino, guanido and ureido radicals? as a blowing agent and heating said stock to a tempera ture sutficient to curethe rubber and form a cellular product, said blowing agent being employed in an amount sutficient to form a cellular product.

2. A process according to claim 1 inwhich the amidine' nitrite is guanylurea nitrite.

3. A process according to claim 1 in whichthe amidine nitrite is guanidine nitrite.

4. A process according to claim in whichth e amidine nitrite is acetamidine nitrite. I

5'. A process according to claim nitrite is biguanide nitrite.

6. An uncured, curable rubber stock containing as a blowing agent.blowingamounts within the'range' of about Parts The mold load is 6 cubic inches and a 200% expansion load 1 in which the dmins 6 i 0.5% to about 5% by weight on the rubber of an amidine 10. A composition according to claim 6 in which'the nitrite of the formula blowing agent is biguanide nitrite.

NH-HNO:

References Cited in the file of this patent R-C-N'Ha in which R is selected from the group consisting of alkyl, UNITED STATES PATENTS aryl, aralkyl, amino, gnanido and ureido radicals. 2,261,459 Cooper et 1941 i 7. A composition according to claim 6 in which the 2,261,677 Foster at 1 blowing agent is guanylurea njtrite 2,635,116 Wolfe et p 1953 8. A composition according to claim 6 in which the 10 25491353 Streck 1953 blowing agent is guanidine nitrite. OTHER REFERENCES 9. A composition according to claim 6 in which the blowing agent is acetamjdine nitrite. Chem volume Page 1915' 

1. A PROCESS OF PRODUCING A CELLULAR RUBBER WHICH COMPRISES FORMING AN UNCURED, CURABLE RUBBER STOCK CONTAINING AN AMIDINE NITRITE OF THE FORMULA 